1. Field of the Invention
The present invention relates to a rod fixing apparatus (a rod fixing structure) fixing a rod portion of a rod member for integrally connecting a vertebra in an acantha, and more particularly to a rod fixing apparatus (a rod fixing structure) to prevent a rod portion of a rod member from being displaced in an axial direction and from being displaced in a rotating direction around an axis.
2. Description of the Related Art
A conventional rod fixing apparatus (fixing structure) is comprised of a screw having a screw portion screwed into a vertebra body in the vertebra, and a head portion integrally provided with the screw. The head portion further includes a groove being engaged with a rod portion of a connection member (a rod member) connecting the separated vertebra bodies, and a rod engagement portion such as an elongated-hole or the like. The rod engagement portion is provided with a pressure fixing device (a fastening screw or the like) for pressure fixing the rod portion engaged with the rod engagement portion.
According to the structure mentioned above, since a position of the rod portion may be displaced with respect to the head portion of the screw, it is necessary to prevent the rod portion from being displaced.
To prevent the rod portion from being displaced, a rod fixing apparatus 103 of a related art (refer to National Publication of Translated Version No. 11-509453) is comprised of a head portion 105 having a screw portion 101 being screwed into the vertebra body (not shown), and the head portion 105 further is comprised of a groove-shaped rod engagement portion 107 having a enlarged-engagement portion 109 being engaged with a enlarged convex rod portion 113 of a rod 111 (refer to FIGS. 1A, 1B).
According to this structure, it is possible to prevent the connection member 111 from being displaced in an axial direction from the rod connecting portion 107 of the head portion 105. However, it is necessary to match a position of the screw 103 and a position of the enlarged convex rod portion 113. Furthermore, it is complicated to manufacture the connection member 111 with the enlarged convex portion 113, and it is impossible to apply the structure to the conventional general rod.